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The structure of Titan’s atmosphere from Cassini radio occultations |
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| Authors: | Paul J Schinder F Michael Flasar |
| Institution: | a Center for Radiophysics and Space Research, Cornell University, Ithaca, NY 14853, USA b NASA Goddard Space Flight Center, Code 693, Greenbelt, MD 20770, USA c Department of Electrical Engineering, San Jose State University, San Jose, CA 95192, USA d Department of Astronomy, Wellesley College, Wellesley, MA 02481, USA e Jet Propulsion Laboratory, Pasadena, CA 91109, USA |
| Abstract: | We present results from the two radio occultations of the Cassini spacecraft by Titan in 2006, which probed mid-southern latitudes. Three of the ingress and egress soundings occurred within a narrow latitude range, 31-34°S near the surface, and the fourth at 52.8°S. Temperature-altitude profiles for all four occultation soundings are presented, and compared with the results of the Voyager 1 radio occultation (Lindal, G.F., Wood, G.E., Hotz, H.B., Sweetnam, D.N., Eshleman, V.R., Tyler, G.L. 1983]. Icarus 53, 348-363), the HASI instrument on the Huygens descent probe (Fulchignoni, M. et al. 2005]. Nature 438, 785-791), and Cassini CIRS results (Flasar, F.M. et al. 2005]. Science 308, 975-978; Achterberg, R.K., Conrath, B.J., Gierasch, P.J., Flasar, F.M., Nixon, C.A. 2008b]. Icarus 194, 263-277). Sources of error in the retrieved temperature-altitude profiles are also discussed, and a major contribution is from spacecraft velocity errors in the reconstructed ephemeris. These can be reduced by using CIRS data at 300 km to make along-track adjustments of the spacecraft timing. The occultation soundings indicate that the temperatures just above the surface at 31-34°S are about 93 K, while that at 53°S is about 1 K colder. At the tropopause, the temperatures at the lower latitudes are all about 70 K, while the 53°S profile is again 1 K colder. The temperature lapse rate in the lowest 2 km for the two ingress (dawn) profiles at 31 and 33°S lie along a dry adiabat except within ∼200 m of the surface, where a small stable inversion occurs. This could be explained by turbulent mixing with low viscosity near the surface. The egress profile near 34°S shows a more complex structure in the lowest 2 km, while the egress profile at 53°S is more stable. |
| Keywords: | Titan Atmospheres Structure |
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